It could well be that you have the dual flush type button that has a screw in the centre, locking the cistern lid down. You have to push one buton down, to allow you to get something underneath the other to flick it out, and then you are able to remove the other one. You will then find a plastic screw in the centre that locks the button housing to the top of the flush valve through the cisatern lid
bob the builder, July 2010
